This invention is directed to a light guiding system, and in particular, to a light guiding system capable of guiding large quantities of energy.
As exemplified by U.S. Pat. No. 247,229, which issued to W. Wheeler on Sept. 20, 1881, the illumination of entire buildings by a central lighting system has long been desired because of its many advantages. The piping of light from a central source brings about efficiencies due to the source size and source location. Such a system allows direct sunlight to be used as a source. In addition, a central lighting system would provide cool light at its outlets with the heat being expended at the source.
Presently, there are two basic techniques of guiding light energy. The first technique, exemplified by U.S. Pat. No. 2,362,175, which issued to H. Swanson on Nov. 7, 1944, employs a dielectric waveguide, which is a solid rod made of transparent material. The light rays are reflected inward by the surface of the rod in a process known as total internal reflection. This process is nearly 100% efficient in containing the light, but unfortunately all reasonably priced transparent materials actually absorb most of the light in relatively short distances, i.e. within a few centimeters to a few meters. The method is therefore used mainly in optical communications systems, where small quantities of extremely expensive dielectric material are used.
In the second technique, light propagates mainly through air, and is periodically redirected to keep it confined and travelling in the correct direction. There are four methods of accomplishing this redirection, including a very recent prism light guide system which is described in U.S. Pat. No. 4,260,220, which issued on Apr. 7, 1981, in the name of Lorne A. Whitehead. This method uses a prism light guide which is made from a longitudinal hollow structure of transparent dielectric material. The walls of the structure are formed such that their inner and outer surfaces are in octature.
In a second method, a hollow pipe with a mirrored inner surface is used to keep the light travelling down the pipe, such a pipe is shown in U.S. Pat. No. 3,700,900, which issued to J. A Herleikson on Oct. 22, 1972.
In a third method which is illustrated in U.S. Pat. No. 3,583,786, issued to E. A. J. Marcatili on June 8, 1971, the pipe consists of an inner cylinder, usually air, surrounded by pairs of dielectric layers wherein the losses are purported to decrease with the number of pairs of layers.
The fourth method is exemplified by U.S. Pat. No. 3,506,331, which issued to R. Kompfner on Apr. 14, 1970, and uses focussing lenses or mirrors at intervals down a hollow pipe.
In a publication by J. W. Y. Lit and D. L. Van Rooy, Appl. Opt. 12, 749, 1973, it is shown that it is possible to guide light energy with a system in which optical elements are restricted to the periphery, as is illustrated in FIG. 1 of the publication. However, in the Lit et al system, the focal points of the lenses lie on the optical axis of the system. In terms of application, the system of Lit et al is suited for guiding light which is diverging principally as a result of diffraction, such as from a laser beam.